Liquid epoxy resins and liquid epoxy resin compositions having inorganic fillers blended in liquid epoxy resins are often employed as encapsulants for flip chips since they are improved in moldability, adherence, electrical and mechanical properties over other conventional thermosetting resins. Such epoxy resin compositions are commercially available in two forms, two part type in which a base resin part and a curing agent part are kept separate and mixed immediately before use and one part type comprising a uniform premix of a base resin and a curing agent. The one part type has been a mainstream in the art since it is easier to use. Prior art one part type epoxy resin compositions formulated as flip chip encapsulants generally use acid anhydrides as the curing agent since the Q compositions must be shelf stable for a long time from their preparation until use. One part type epoxy resin compositions using curing agents other than acid anhydrides are less stable during storage.
Epoxy resin compositions incorporating acid anhydrides, however, have several drawbacks. The compositions tend to absorb moisture which causes the compositions to expand in volume, adversely affecting flip chip characteristics, especially the resistance at the solder bump-lead interface. Thermal changes during curing and thermal changes in the service environment also increase the resistance at the solder bump-lead interface. Although flip chip encapsulation requires that the encapsulant fill in spaces as narrow as about 20 to 100 .mu.m, the compositions are too viscous or thixotropic to achieve complete filling.
Therefore, an object of the present invention is to provide a flip chip encapsulating composition of the one part type having improved shelf stability and filling ability and curing into products having improved moisture resistance. Another object of the present invention is to provide a semiconductor device encapsulated therewith.